1. Field of the Invention
The present invention relates to a dynamic pressure bearing apparatus for a spindle motor used with information equipments, acoustic equipments or imaging equipments, particularly for a spindle motor suitable for optical disc devices and magnetic disc devices, and, a dynamic pressure bearing apparatus for a fan motor, particularly using a radial/thrust integral resin bearings, and more particularly, it relates to a dynamic pressure bearing apparatus for a fan motor, which has excellent performance and endurance and which can easily be worked and assembled.
2. Related Background Art
Conventionally, although a bearing apparatus utilizing a sliding bearing or a ball bearing has been used in such a system, recently, due to request for high speed transferring of data, higher speed rotation of a rotary member (shaft) has been requested. As a result, there arose a problem that whirling of the rotary member is increased by the influence of a centrifugal force. To minimize an amount of the whirling, a dynamic pressure bearing apparatus (dynamic pressure spindle motor) utilizing a dynamic pressure bearing has been used.
An example of a conventional dynamic pressure bearing apparatus is shown in FIG. 15 which is a sectional view. FIG. 16 is an enlarged view showing a bearing member of FIG. 15. In this conventional example, a bearing member 1004 defines a cylindrical bore 1013 including a metallic sleeve 1002 and a thrust bearing member 1003, and the sleeve 1002 has an inner diameter surface 1009 which is provided with dynamic pressure generating grooves 1014 to define a radial bearing surface 1010. In the thrust bearing member 1003 connected to the sleeve 1002, a thrust bearing surface 1012 defining a part of the cylindrical bore 1013 has a convex spherical shape to provide a sliding bearing. The thrust bearing member 1003 has a vent hole 1005. A turn table 1015 is attached to a shaft 1007 which is driven by a rotor 1018 and a stator 1019.
In the dynamic pressure generating grooves 1014, when it is assumed that axial lengths from bent portions to upper (open) sides are A, C and axial lengths from the bent portions to lower (bottom) sides are B, D, relationships A greater than B, C greater than D and (A+C) greater than (B+D) are established, and, thus, the grooves are asymmetrical in the axial direction. The reason is that, by generating axial load capacity, a thrust force for floating the shaft 1007 (rotor) is generated to prevent the bearing portions (particularly, lower portion of the radial bearing and the thrust bearing) from being subjected to negative pressure. If the bearing portions are subjected to the negative pressure, the whirling (of the shaft) will be generated to worsen bearing performance.
On the other hand, since the thrust bearing surface 1012 has the vent hole 1005 at its one end, when the shaft 1007 is inserted into the bearing, lubricating oil leaks through the vent hole 1005, thereby not ensuring reservation of the lubricating oil. Further, in an inoperative condition of the bearing after insertion of the shaft 1007, if an environmental temperature is increased, viscosity of the lubricating oil is decreased, and the lubricating oil may leak through the vent hole 1005.
To prevent the leakage of the lubricating oil, there has been proposed a dynamic pressure bearing apparatus (not shown) of type which has similar construction as that shown in FIG. 16 but has no vent hole 1005 in the thrust bearing member 1003.
However, in the type having no vent hole 1005, when the bearing is operated, oil in an oil reservoir 1008 is sucked toward the bottom, which causes a new problem that the rotary members (shaft, rotor, turn table, disc) are floating above the thrust bearing surface 1012. It is very difficult to suppress such floating particularly when a circumferentially opposed motor (in which a rotor 1018 and a stator 1019 are opposed to each other in a radial direction) is used.
A floating amount of the rotary members depends upon an amount of oil in the oil reservoir 1008.
In a disc driving system, in which a disc 1016 rotated, when the disc is floating due to rotation of the drive, a gap between the disc and a recording/reproducing head is decreased to make recording/reproducing impossible. The space (gap) between the recording/reproducing head and the surface of the disc in the disc driving system must be maintained with high accuracy. Thus, some control for the floating amount of the shaft is required in the bearing apparatus.
However, for this requirement, the floating of the rotor cannot be prevented by using the above-mentioned groove pattern.
On the other hand, an example of a conventional fan motor used in office equipments is described in Japanese Utility Model Registration No. 2553251. FIG. 17 is a sectional view showing a conventional dynamic pressure bearing apparatus for a fan motor. A rotor 2031 is secured to an inner peripheral surface of a support member 2033, and vanes 2030 are secured to an outer peripheral surface of the support member 2033. The rotor 2031 is constituted by a magnet 2032. The support member 2033 is secured to one end of a rotary shaft 2037 having a dynamic pressure generating portion (dynamic pressure generating grooves 2036). A cylindrical sleeve 2035 is mounted on a central portion of a case 2039, and a stator 2034 is secured to an outer peripheral surface of the sleeve 2035 in a confronting relation to the rotor 2031. Below the sleeve 2035, a resin receiver member 2040 for supporting the rotary shaft 2037 is attached to the case 2039. A dynamic pressure bearing 2038 is constituted by rotatably fitting the rotary shaft 2037 into the sleeve 2035, and a cylindrical space formed between the sleeve 2035 and the rotary shaft 2037 is filled with grease 2041. The vanes 2030 and the rotor 2031 are supported in the radial direction via the dynamic pressure bearing 2038 so that the vanes 2030 and the rotor 2031 can be rotated around the stator 2034. That is to say, the rotor 2031 is rotated by a rotational magnetic field generated by the stator 2034 to rotate the vanes 2030 (in a direction shown by the arrow Z in FIG. 17), thereby generating air streams directing toward a direction shown by the arrow X to effect air blast. A thrust load (shown by the arrow Y) acting on the rotary shaft 2037 as a thrust force generated by rotation of the vanes 2030 (reaction force of the blasting operation) is supported by an axial component of an attracting force acting between an iron core (not shown) of the stator 2034 and the magnet 2032 of the rotor 2031. The stator 2034 and the rotor 2031 are offset in the axial direction so that the attracting force becomes greater than the thrust force generated by the rotation of the vanes 2030 by a predetermined rate. By the remaining axial component thrust load obtained by subtracting the thrust force of the vanes 2030 from the attracting force acting between the stator 2034 and the rotor 2031, an end surface of the rotary shaft 2037 is urged against the resin receiver member 2040 of the case 2039 to support the rotary shaft.
However, in the conventional bearing for the fan motor, since the number of parts of the bearing is increased (i.e., becomes two; radial bearing and thrust receiver member (resin receiver member 2040)), the assembling steps are increased and the construction of the bearing becomes complicated. Further, since perpendicularity of the end surface of the rotary shaft 2037 supporting the thrust load must be maintained with high accuracy, the apparatus cannot be made cheaper. In addition, since the end surface of the shaft and the surface of the receiver member which support the thrust load are flat, the peripheral edge of the end surface of the shaft contacts with the surface of the receiver member to easily damage the latter. Further, since the rotor 2031 is attracted in the axial direction by the magnetic force opposite to the thrust force of the vanes 2030 (in the axial direction) by offsetting the stator 2034 with respect to the rotor 2031 in the axial direction so as to become the axial component of the attracting force acting between the iron core of the stator 2034 and the magnet 2032 of the rotor 2031 greater than the thrust force of the vanes 2030, the axial dimension becomes great and precludes compactness (thinness) of the apparatus. Also, since the stator 2034 is greatly offset with respect to the rotor 2031 in the axial direction, the rotary shaft 2037 and the vanes 2030 are apt to be vibrated and noise is apt to be generated.
Further, since the thrust force generated by the rotation of the vanes 2030 is increased as the number of rotations of the vanes is increased, the magnet 2032 must generate the opposite magnetic force greater than the thrust force generated during steady-state rotation. In this case, in low speed rotation generating smaller thrust force of the vanes 2030, a greater thrust load acts on the thrust receiver member to wear the latter. In addition, since the grease is used as the lubricating agent, it is difficult to expel the air from the interior of the bearing when the rotary shaft 2037 is inserted. Thus, a relatively large amount of air remains within the bearing, which results in reduction of performance of the dynamic pressure bearing and increased torque.
The present invention aims to eliminate the above-mentioned conventional drawbacks and has been created on the basis of a new technique.
A first object of the present invention is to provide a dynamic pressure bearing apparatus comprising a cylindrical bearing member, and a rotary shaft disposed within a cylindrical bore of the cylindrical bearing member, and wherein the bearing member has a thrust bearing surface provided at a bottom of the cylindrical bore, a radial bearing surface provided on an inner peripheral surface of the cylindrical bearing member, and a lubricating oil reservoir provided at an opening portion of the cylindrical bore and having a diameter greater than that of the radial bearing surface, and the rotary shaft has a radial receiving surface opposed to the radial bearing surface with the interposition of a radial bearing gap, and a thrust receiving surface opposed to the thrust bearing surface, and further wherein the bearing member is closed at the bottom thereof, a dynamic pressure generating groove is formed in at least one of the radial bearing surface and the radial receiving surface, and the dynamic pressure generating groove generates a force for flowing lubricating oil between the bearing member and the rotary shaft toward the opening portion of the cylindrical bore.
In a first embodiment of the present invention, since the radial bearing gap is closed at the bottom, the lubricating oil is surely loaded within the bearing without leakage, and, since the dynamic pressure generating grooves of the radial dynamic pressure bearing are constituted as grooves to generate a thrust force for urging the shaft against the thrust bearing surface, a dynamic pressure bearing apparatus for a spindle motor, in which the shaft is not floating regardless of a rotational speed of the shaft can be realized.
From an investigation of the dynamic pressure bearing apparatus according to the present invention, optimum values of an outer diameter of the rotary shaft, the radial bearing gap and axial lengths of the dynamic pressure generating grooves were determined concretely.
Thus, the present invention provides a dynamic pressure bearing apparatus wherein an outer diameter of the rotary shaft is 2 mm to 5 mm, and the radial bearing gap is 3 xcexcm to 10 xcexcm, and each of the dynamic pressure generating grooves has a laid V-shaped configuration in which a ratio between an axial length of a groove portion extending from a bent portion of xe2x80x9cVxe2x80x9d toward the opening portion of the cylindrical bore and an axial length of a groove portion extending from the bent portion toward the bottom of the cylindrical bore is selected to 15:16 to 3:4.
By selecting the values of the outer diameter of the rotary shaft, the radial bearing gap and the ratio of the axial lengths of the dynamic pressure generating grooves to the above-mentioned concrete values, a dynamic pressure bearing apparatus can be realized in which the shaft is not floating regardless of a rotational speed of the shaft and in which substantially no non-rotational component (including whirling) is generated.
A second object of the present invention is to provide a dynamic pressure bearing apparatus for a fan motor, which has a simple construction and can be made compact while adequate performance can nonetheless be ensured.
According to a second embodiment of the present invention, there is provided a dynamic pressure bearing apparatus for a fan motor, comprising a radial/thrust integrating resin sleeve having a radial bearing portion including dynamic pressure generating grooves formed in an inner surface of the cylindrical portion formed by injection molding, and a thrust bearing portion contiguous to the radial bearing portion and formed on a bottom of the cylindrical portion. By constituting the dynamic pressure bearing by the radial/thrust integrating resin sleeve in this way, since manufacture is facilitated and the number of parts is reduced and assembling is also facilitated, the entire bearing apparatus can be made cheaper.
Particularly, when the dynamic pressure generating grooves (radial dynamic pressure bearing portion) formed in an inner surface of the cylindrical portion of the sleeve have a groove pattern capable of supporting a load in a radial direction and generating a force acting toward a direction opposite to a direction of a thrust force of vanes, a construction can be made simpler and an axial dimension can be reduced, whereby the entire apparatus can be made more compact (thinner). More specifically, the design may be such that a lower width of the groove pattern is greater than an upper width of the groove pattern. With this arrangement, since it is not required that the stator is greatly offset from the rotor in the axial direction, the vanes are not readily vibrated in the axial direction and occurrence of noise is prevented. Alternatively, the dynamic pressure generating grooves may be also formed in the rotary shaft. In this case, the rotary shaft becomes a dynamic pressure bearing portion having the dynamic pressure generating grooves formed in the outer peripheral surface of the shaft, which gives the same advantage as the dynamic pressure generating grooves formed in the sleeve.
Further, when the radial/thrust integrating resin sleeve is used and one of a free end surface of the rotary shaft and the thrust bearing surface has a spherical face to support the thrust load in a point contact fashion, low friction is ensured, so that the thrust bearing surface is not damaged by the edge of the shaft. More specifically, a convex spherical face may be formed on a thrust receiving member at the bottom of the resin sleeve to support the end surface of the rotary shaft, or a convex spherical face may be formed on the end surface of the rotary shaft to be supported by the thrust receiving member at the bottom of the resin sleeve. Since the radial bearing is also formed from resin, starting friction resistance can be reduced (the shaft is contacted with the inner surface of the sleeve at the starting and stopping), thereby ensuring low friction to achieve excellent wear-resistance in the entire bearing apparatus. Resin materials having great strength and excellent wear-resistance are preferable, but, the resin is not limited to specific resin material. For example, the resin may be PPS (polyphenylene sulfide resin) including carbon fibers. By using the oil as the lubricating agent, air in the bearing can easily be expelled during insertion of the rotary shaft. Thus, since almost no air remains within the bearing, performance of the dynamic pressure bearing is preserved. When the oil is used as the lubricating agent, torque can be reduced in comparison with grease.
In the second embodiment, the dynamic pressure bearing apparatus for a fan motor comprises a cylindrical bearing member, and a rotary shaft disposed within a cylindrical bore of the cylindrical bearing member and having one end rotatably supporting a vane and a rotor and the other end being a free end. The bearing member has a thrust bearing surface provided at a bottom of the cylindrical bore, a radial bearing surface formed on an inner peripheral surface of the cylindrical bearing member, and a lubricating oil reservoir provided at an opening portion of the cylindrical bore and having a diameter greater than that of the radial bearing surface; a stator is disposed around the bearing member in a confronting relation to the rotor; and the bearing member is made of resin and is closed at its bottom. A dynamic pressure generating groove is formed in at least one of the radial bearing surface and a radial receiving surface to direct the thrust force generated by the rotation of the vane toward the thrust bearing surface; and a spherical face is formed on one of the free end of the rotary shaft and the thrust bearing surface.
In the dynamic pressure bearing apparatus for a fan motor, the dynamic pressure generating groove has a groove pattern for generating a force directing toward an axial direction opposite to a direction of the thrust force generated by rotation of the vane, and the axial force generated by the dynamic pressure generating groove is smaller than the axial force generated by the rotation of the vane.
A further object of the present invention is to provide a dynamic pressure bearing apparatus for a fan motor, which has excellent performance and endurance and can easily be worked and in which the number of parts is small to facilitate assembling and to make the entire apparatus cheaper.
A still further object of the present invention is to provide a dynamic pressure bearing apparatus for a fan motor, in which a thrust load in a thrust bearing portion is reduced to achieve low torque and low friction.
In a further embodiment of the present invention, there is provided a dynamic pressure bearing apparatus for a fan motor, comprising a radial/thrust integrating resin sleeve having a radial dynamic pressure bearing portion including dynamic pressure generating grooves formed in an inner surface of the cylindrical portion formed by injection molding, and a thrust bearing portion contiguous to the radial bearing portion and formed on a bottom of the cylindrical portion, which can easily be worked and assembled and in which the number of parts is small. Since a thrust force generated by rotation of vanes is directed toward the thrust bearing portion, it is not required that a force for attracting a rotor in an axial direction becomes greater than the thrust force. Since blasted air generated by the rotation of the vanes acts on upper sides of the vanes, the thrust load acting on the rotary shaft is directed toward the thrust bearing portion (for urging the rotary shaft against the thrust bearing surface). Thus, it is not required that the stator is greatly offset from the rotor in the axial direction. Since the radial bearing is also formed from resin, starting friction resistance can be reduced (the shaft is contacted with the inner surface of the sleeve at the starting and stopping). By using the oil as the lubricating agent, air in the bearing can easily be expelled during insertion of the rotary shaft. Thus, since almost no air remains within the bearing, performance of the dynamic pressure bearing is preserved. When the oil is used as the lubricating agent, torque can be reduced in comparison with grease.
When the radial/thrust integrating resin sleeve is used as the resin sleeve and one of the free end surface of the rotary shaft and the thrust bearing surface has the spherical face to support the thrust load in the point contact fashion, it is not required that perpendicularity of the end surface of the rotary shaft supporting the thrust load is maintained with high accuracy. More specifically, the convex spherical face may be formed on the thrust receiving member at the bottom of the resin sleeve to support the end surface of the rotary shaft, or the convex spherical face may be formed on the end surface of the rotary shaft to be supported by the thrust receiving member at the bottom of the resin sleeve. Resin materials having great strength and excellent wear-resistance are preferable, but, the resin is not limited to specific resin material. For example, the resin may be PPS (polyphenylene sulfide resin) including carbon fibers.
In a still further embodiment of the present invention, there is provided a dynamic pressure bearing apparatus for a fan motor, wherein dynamic pressure generating grooves formed in an inner surface of a resin sleeve have a groove pattern for generating an axial force acting toward a direction opposite to a thrust force generated by rotation of vanes of the fan motor. When the axial force generated by the dynamic pressure generating grooves is smaller than the axial force generated by the rotation of the vanes and the remaining thrust load obtained by subtracting the axial force generated by the dynamic pressure generating grooves from the thrust force generated by the rotation of the vanes acts on the end surface of the rotary shaft and the thrust bearing surface, the thrust load acting on the thrust bearing portion can be reduced.
Particularly, when the dynamic pressure generating grooves (radial dynamic pressure bearing portion) formed in the inner surface of the cylindrical portion of the sleeve have the groove pattern capable of supporting a load in a radial direction and generating the force acting toward the direction opposite to the direction of the thrust force generated by the rotation of the vanes, since a construction can be made simpler and an axial dimension can be reduced, the entire apparatus can be made more compact (thinner). More specifically, the design is such that an upper width of the groove pattern is greater than a lower width of the groove pattern. With this arrangement, since it is not required that the stator is greatly offset from the rotor in the axial direction, the vanes are not readily vibrated in the axial direction during the rotation of the vanes and occurrence of noise is prevented.
In a third embodiment of the present invention, the dynamic pressure bearing apparatus for a fan motor comprises a cylindrical bearing member, and a rotary shaft disposed within a cylindrical bore of the cylindrical bearing member and having one end rotatably supporting a vane and a rotor and the other end being a free end. The bearing member has a thrust bearing surface provided at a bottom of the cylindrical bore, a radial bearing surface formed on an inner peripheral surface of the cylindrical bearing member, and a lubricating oil reservoir provided at an opening portion of the cylindrical bore and having a diameter greater than that of the radial bearing surface; a stator is disposed around the bearing member in a confronting relation to the rotor; and the bearing member is made of resin and is closed at its bottom. A dynamic pressure generating groove is formed in at least one of the radial bearing surface and a radial receiving surface to direct a thrust force generated by the rotation of the vane away from the thrust bearing surface; and a spherical face is formed on one of the free end of the rotary shaft and the thrust bearing surface.
In the dynamic pressure bearing apparatus for a fan motor according to this embodiment, the dynamic pressure generating groove has a groove pattern for generating a force directing toward an axial direction opposite to a direction of the thrust force generated by the rotation of the vane, and the axial force generated by the dynamic pressure generating groove is greater than the axial force generated by the rotation of the vane.